1. Field of the Invention
This invention generally relates to an air intake control device. More specifically, the invention relates to a throttle body and a method of assembling a throttle body.
2. Description of the Related Art
Throttle bodies regulate the airflow to an internal combustion engine. In order to run properly, internal combustion engines require a precise mixture of air and gasoline and, therefore, throttle bodies are designed to adjustably control the airflow into the cylinders of the engine. In order to control the airflow that reaches the cylinders, the throttle body includes at least one throttle plate attached to a throttle shaft such that the throttle plate is located within a throttle bore, or proximal to an end of the throttle bore. With rotation of the shaft, the throttle plate is able to selectively obstruct airflow through the throttle bore. More specifically, the throttle plate is able to rotate with respect to the bore in order to adjust the cross-sectional area of the bore that is not obstructed by the plates (the “effective area”), thus controlling the amount of airflow that is permitted to flow through the throttle bore.
In order to effectively control the effective area, the throttle plate is sized and shaped to approximate the cross-sectional area of the bores so as to substantially or completely obstruct the bore when the throttle plate is perpendicular to the airflow (the “closed position”). Additionally, the throttle plate has a minimal thickness in order to substantially not obstruct the throttle bore when the plate is angled such that a throttle plate is not substantially perpendicular to the airflow (the “open position”).
During operation, if the engine is idling, only a little air is needed to mix with the small amount of fuel being injected into the engine. When the engine is idling, the throttle plate is therefore in the closed position. Conversely, if the engine is operating at a speed higher than! idle, then more air is needed to mix with the increased amount of fuel being provided to the engine. At speeds higher than idle, the throttle plate is therefore in an open position of a varying angle with respect to the airflow, the angle varying within the air requirements.
In order to completely or substantially obstruct the bore when the throttle plate is the dosed position, it is desirable for the throttle plate to be precisely sized and accurately located within the bore.
Furthermore, it is desirable for the throttle plate to be secured in the direction parallel to the rotational axis of the throttle shaft (referred to as the longitudinal direction). This minimizes or prevents unwanted contact between the throttle plate and the bore inner surface. Contact between the throttle plate and the bore inner surface may prevent the throttle plate from fully closing. Furthermore, contact may cause excessive friction between moving parts and premature part failure. The control of the longitudinal movement of the throttle plate is hereinafter referred to as float control.
In order to improve float control, some currently-used throttle bodies include a first press-fit connection between the throttle shaft and an inner race of a bearing, and a second press-fit connection between the outer race of the bearing, and the throttle body housing. However, the first press-fit connection may deform the throttle shaft during periods of assembly or maintenance of the throttle body. Throttle shaft deformation is undesirable because it may prevent the throttle shaft from being reusable after assembly or maintenance, thus potentially increasing assembly and/or service costs.
Another float control method includes an assembly for longitudinally trapping the inner race of the bearing in a predetermined position on the throttle shaft. More specifically, the inner race is sandwiched between a first structure, such as a threaded nut, on a first longitudinal side of the bearing and a second structure, such as a stepped-diameter of the throttle shaft, on a second longitudinal side of the bearing. However, this type of float control construction may require complicated machining operations and part requirements.
Yet another float control method includes an clip located in a groove for longitudinally trapping the inner race of the bearing in a predetermined position on the throttle shaft. More specifically, the clip is seated in a groove such as to contact the bearing on a first longitudinal side and such that the second longitudinal side of the bearing contacts the housing. However, this type of float control construction may require complicated machining operations and may result in undesirable, high-frictional contacts between the respective structures and the bearing.
Therefore, it is desirous to minimize both the longitudinal movement of the throttle shaft and the friction between moving parts, all while reducing the manufacturing and assembly costs and complexities of the throttle body.